Federal officials have estimated that the drilling would take four days, after which mud and cement would be pumped in to plug the BP well for good.

Crews began drilling through the remaining 50 feet of rock Monday afternoon to complete the final "bottom kill" plug of BP's troubled Gulf of Mexico oil spill.

Federal officials have said it should take about four days to drill the final stretch of the relief well so that it intersects with the original well. From there, it will probably take a few days to pump in mud and cement and perform tests to determine that the well is fully killed.

The well spewed an estimated 4.9 million barrels of oil into the gulf before it was fitted with a temporary sealing cap in mid-July. Since then, it has received an initial shot of mud and cement and a new blowout preventer as part of the effort to ensure that it does not leak again. But the bottom kill has long been touted as the ultimate solution to the problem.

On land, meanwhile, compensation fund administrator Ken Feinberg said Monday that he may reconsider a controversial rule that subtracts cleanup wages from residents' spill claims against BP.

"I'm taking it under advisement," Feinberg said at a town hall meeting in Houma, La. "The last time I said, no way, I'm deducting it. Now, it's open for discussion."